The present invention relates to an extended bandwidth folded well diffusor. The acoustic performance of diffusors at low frequencies is limited by the size of the diffusor compared to the wavelength of sound. There are generally two distances of importance, the maximum displacement of the diffusor (the diffusor depth), and, if the diffusor is periodic, meaning there are many identical diffusors side-by-side, then the repeat distance between adjacent identical diffusors can also be significant.
As understood by those of ordinary skill in the art, the term “diffusor” as used throughout this text and the claims has the following meaning: “an acoustical device located in a room or space and that receives sound waves from the room or space and is designed to scatter or diffuse those sound waves back into the room or space in a predetermined way based upon design of the diffusor's wells and recesses.”
The limitation imposed by repeat distance can be overcome by having no repetition in the device, or by using a modulation scheme. However, the depth available for treatment is often limited. Ultimately, the designer or architect will typically limit the depth available for acoustic treatment, although sometimes the maximum depth is restricted because of concerns about absorption. In any case, with the wavelength of audible sound extending to 17 m (55.8 feet), it is impossible to construct a practical diffusor that will cover the full audible bandwidth with low absorption, and is also usable in most rooms. Consequently, there is always interest in methods for extending the bandwidth of diffusing devices to a lower frequency without making the device deeper.
Previously, various authors have suggested bending the wells of Schroeder diffusers to extend the frequency range over which the well perturbs the sound wave. Also, the folded wells utilize the wasted space at the rear of the diffusor, and so produce more low frequency dispersion. Results have demonstrated that the diffusor with folded wells enables diffusion to occur at a lower frequency from a given maximum depth. As the frequency increases, however, the apparent depth of the folded well changes as most of the sound wave no longer propagates around the bend.
The problem with the folded well construction is the cost of manufacture. Consequently, it has not been often commercially exploited. In addition, shallow diffusers, with a thickness of 1 or 2″, are typically molded from a solid block of hardwood, plastic or solid surface material, which is found visually attractive. In these situations, it is not possible to form folded wells in the interior of the diffusor without a secondary operation forming the L-shaped well. The present invention contemplates a new method and design methodology to achieve an asymmetric, bended-well diffusor, which is easy to make and easy to aperiodically modulate.